Yes I was always dreaming of making a doom like with my own settings, and then CTHON showed off ( I wouldn't make a better game,and I love it)
I’d say you ought to still give it a try! Just because something similar already exists or is done well does not mean someone can’t do it better or differently, and there are certainly things about CTHON I could have done better on. CTHON was written in Game Maker as well, which is pretty easy to jump into and start using!